Heretofore, as rolling bearings with sensor there have been those disclosed in JP-A-63-111416, JP-A-7-325098, JP-A-7-311212, JP-A-10-311740, etc.
The rolling bearing with sensor disclosed in JP-A-63-111416 comprises a magnetic material layer having a predetermined patterned magnetization provided on either one of the opposing surface of the inner ring and the outer ring and a magnetism sensor mounted on the other. The magnetic material layer has a plurality of patterned magnetized portions provided circumferentially.
The rolling bearing with sensor disclosed in JP-A-7-325098 comprises a magnetized portion provided on the rotary ring and a magnetism sensor proved on the stationary ring as in the aforementioned publication and has an increased clearance between the inner ring and the outer ring to provide an increased space in which the magnetized portion and sensor are received.
All these structures comprise a sensor mounted on the outer ring which is a stationary ring with a retaining member and a detection member such as multipolar magnet mounted on the inner ring which is a rotary ring.
Further, FIG. 45 illustrates a rolling bearing 1090 with sensor disclosed in JP-A-7-311212. The rolling bearing 1090 comprises balls 1093 rollably retained between an outer ring 1091 and an inner ring 1092. On one axial side is provided a seal member 1094. On the end surface opposite the seal member 1094, a sensor 1096 is provided on the outer ring 1091 with a retaining member 1095 and a detection member 1099 is provided on the inner ring 1092 with a retaining member 1098.
The retaining member 1095 mounted on the outer ring 1091 has a mounting portion 1095a fitted on the inner surface of the outer ring 1091, a flange portion 1095b connected to the mounting portion 1095a extending outward radially and a sensor retaining portion 1095c connected to the flange portion 1095 extending axially. The flange portion 1095b covers the entire area of the end surface of the outer ring 1091. On the inner surface of the sensor retaining portion 1095c is retained the sensor 1096.
The retaining member 1098 mounted on the inner ring 1092 is formed having an L-shaped section comprising a cylindrical portion fitted on the outer surface of the inner ring 1092 and a detection member retaining portion extending outward radially from the cylindrical portion and retains the detection member 1099 in such an arrangement that the detection member 1099 is axially opposed to the sensor 1096 with a slight clearance therebetween.
In general, a bearing with sensor is used as a rotary state detecting device of detecting the speed, direction or angle of rotation of a rotary body such as bearing. A rotary state detecting device comprises a rotation sensor provided outside the rotary body and detection members disposed periodically on the surface of the rotary body. The rotation sensor calculates the speed, direction or angle of rotation of the rotary body on the basis of the period of detection of the detection material and the period of disposition of the detection material.
JP-A-9-42994 discloses a slewing bearing comprising a slewing angle detector. This slewing angle detector comprises a scale and a sensor each mounted on the inner ring and the outer ring which are bearing rings. The scale has N poles and S poles alternately arranged along the circumference of the shaft. The sensor senses the magnetic force of N poles and S poles to detect pulse signals and counts the number of pulse signals. The signal converting unit converts pulse signal to angle data according to the number of pulse signals and displays the angle data.
JP-A-7-218239 discloses a bearing with rotary angle detector comprising a lattice pattern provided on the rotary ring of the bearing, a plurality of LED's provided opposed to the lattice pattern and a plurality of PD's of detecting light which has been emitted by a light source and modified by the aforementioned pattern. The light emitted by the plurality of LED's each form a beam spot on the lattice pattern. The beam spot shows a periodical change of intensity of reflected light due to the dark and bright portions of the lattice pattern. The plurality of PD's each observe the change of intensity of reflected light and calculates the rotary angle of the shaft according to the results of observation.
JP-A-7-218248 discloses a contact type rotary angle detecting device. This rotary angle detecting device comprises an insulating material layer provided on the end surface of an outer ring, a conductor pattern provided on the insulating material layer and a contactor provided on an inner ring opposed to the conductor pattern. The contactor comes in contact alternately with the conductor pattern and the insulating material with the rotation of a rotary body. The conductor pattern is short-circuited and conducted when brought into contact with the contactor. The rotary angle detecting device detects the rotary angle of the rotary body by the presence/absence of conduction of the conductor pattern to the contactor.
Further, JP-A-2000-346673 discloses a rotary speed detecting device comprising magnets disposed on the circumference of a rotary body and a single magnetism sensor disposed in the vicinity of the rotary body which detects the magnetic flux formed by the magnets. The rotary body has a plurality of N poles, S poles and nonpolar sets provided therein in sequence and the magnetism sensor detects the magnetic force of the N poles, S poles and nonpolar sets to detect the rotary speed of the rotary body. In addition, the magnetism sensor measures the direction of rotation of the rotary body on the basis of the order of detection of magnetic poles (“N pole—S pole—nonpolar set” or “nonpolar set—S pole—N pole”) This rotary speed detecting device can measure the speed and direction of rotation of the rotary body using a single magnetism sensor and thus doesn't need to provide another sensor therein and is advantageous in the reduction of the size of bearing.
However, when the outer ring 1091 of a rolling bearing 1090 with sensor as shown in FIG. 45 is axially pressed with a sensor 1096 interposed therebetween so that a load is applied thereto as shown by the arrow P to press it into a housing, the clearance between the sensor 1096 and a detection member 1099 can be deviated, making it impossible to accurately detect the number of revolutions or the like. Further, a load P can be applied to set a pilot pressure for the rolling bearing 1090, occasionally causing the deviation of the clearance of the sensor 1096 and the detection member 1099. The clearance between a retaining member 1095 and the sensor 1096 is normally molded by a resin to fix the sensor 1096 and thus can be easily damaged or deformed by a load P.
Moreover, since the clearance between the inner ring and the outer ring of a bearing is normally small, it is necessary that the sensor or the opposing detection member be formed thin. However, since the sensor is provided integrally with a board for mounting the sensor, it is difficult to reduce the thickness of the sensor to a predetermined limit or less. The above cited JP-A-63-111416 proposes that a magnetic material layer integrated to an inner ring or outer ring be provided to reduce the thickness of the detection member, but the formation of such a layer requires a special technique that causes the increase of the production cost.
The above cited JP-A-7-325098 proposes that the clearance between the inner and outer rings be raised to simplify the configuration of the magnetism sensor or detection member, but a plurality of sensors must be axially arranged in parallel, increasing the width of the entire bearing.
Further, when a rolling bearing with sensor is disposed in the vicinity of an apparatus which generates magnetic flux such as electric motor and high frequency power supply, magnetic flux leaked from such an apparatus affects the circuit constituting the sensor, occasionally causing erroneous operation of the sensor. Moreover, in the case where an apparatus having its alternating power supply grounded via the housing thereof is used with the aforementioned rolling bearing with sensor attached thereto, if the housing is insufficiently grounded, the voltage of the alternating power supply is applied also to the sensor. This is accompanied by the flow of weak current through the sensor, occasionally causing the mixing of the output signal of the sensor with noise attributed to the frequency of the power supply, etc.
Further, in the case of JP-A-2000-346673, for the reason of failure or replacement of memory storing the angle before the starting of rotation, the angle data during the starting of rotation can be lost. In this case, it is disadvantageous in that relative reference position is lost, making it impossible to calculate absolute angle unless reference angle is reset.